1. Field of the Invention
This invention relates to a laser diode pumped solid state laser. This invention particularly relates to a laser diode pumped solid state laser, wherein the wavelength of a laser beam, which has been obtained from solid state laser oscillation, is converted into a different wavelength, e.g., is shortened, by using a nonlinear optical material, and wherein generation of a laser beam in a single longitudinal mode is enabled by injection rocking.
2. Description of the Prior Art
Laser diode pumped solid state lasers have been proposed in, for example, Japanese Unexamined Patent Publication No. 62(1987)-189783. The proposed laser diode pumped solid state lasers comprise a solid state laser medium, which has been containing a rare earth metal, such as neodymium (Nd). The solid state laser medium is pumped by a semiconductor laser (a laser diode). In the laser diode pumped solid state laser of this type, in order for a laser beam having as short a wavelength as possible to be obtained, a bulk single crystal of a nonlinear optical material for converting the wavelength of a laser beam, which has been obtained from solid state laser oscillation, is located in a resonator of the solid state laser. The laser beam, which has been obtained from the solid state laser oscillation, is thereby converted into its second harmonic, or the like.
In cases where such a laser diode pumped solid state laser is used, it is desired that a laser beam, the wavelength of which has been shortened, be obtained with a stable output power. However, with the conventional laser diode pumped solid state lasers, a laser beam having a stable output power cannot always be obtained because of longitudinal mode competition of the laser beam, which has been obtained from the solid state laser oscillation.
Therefore, for the purposes of achieving solid state laser oscillation in a single longitudinal mode, it has heretofore been proposed to provide a semiconductor laser for injection locking independently of a semiconductor laser for producing a pumping laser beam. In such cases, a laser beam, which has been produced by the semiconductor laser for injection locking, is caused to impinge upon a solid state laser medium for injection locking, and the solid state laser medium for injection locking is pumped. A laser beam, which has thus been obtained from the solid state laser medium for injection locking in the single longitudinal mode, is then caused to impinge upon a primary solid state laser medium, which is independent of the solid state laser medium for injection locking. With such a technique, injection locking is effected in the primary solid state laser medium by the laser beam for injection locking, and the solid state laser is caused to oscillate in the single longitudinal mode.
However, with the technique described above, it is necessary to provide the semiconductor laser for injection locking. Also, it is necessary to provide a beam splitter, mirrors, or the like, for combining the laser beam for injection locking and the pumping beam with each other. Therefore, the problems occur in that, because the number of parts required increases, the cost of the solid state laser cannot be kept low, its reliability cannot be kept high, and assembly and adjustment processes become complicated.